JP2020200194A - Manufacturing method of diamond substrate - Google Patents

Abstract

To provide a method for manufacturing a diamond substrate efficiently.SOLUTION: A manufacturing method of a diamond substrate includes following steps: a formation step, for forming a diamond layer on a support substrate to obtain a composite substrate; a processing step, for processing the composite substrate at an approximately same temperature as the support substrate in the formation step to obtain processed substrate; and a separation step, for separating the support substrate from the processed substrate, to thereby obtain a diamond substrate comprising the diamond layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a diamond substrate.

Diamond has excellent properties such as high thermal conductivity, high hardness, wide bandgap, and high transparency, and is therefore useful as a material for heat diffusion applications, processing applications, power semiconductor substrates, high-intensity laser window materials, and the like. ..

In the heat diffusion application, a diamond heat sink and a heat diffusion substrate having a metal plate on the surface of a diamond polycrystal are known. These are used in an appropriate size of a few mm square to fit the device mounting process.

Diamonds are artificially produced by various methods. For example, a high-temperature and high-pressure method as disclosed in Patent Document 1, a vacuum film formation by a CVD method as disclosed in Patent Document 2, and the like can be mentioned. Further, Patent Document 3 discloses an example in which diamond is molded by laser cutting.

Japanese Unexamined Patent Publication No. 56-140017 Japanese Patent Publication No. 2004-503460 JP-A-2009-167070

In the production of a diamond substrate by the CVD method, (1) the raw material gas of diamond is decomposed by heat or plasma to form a diamond layer on the prepared support substrate, and (2) the forming step is obtained. A processing process in which a composite substrate having a diamond layer and a support substrate is laser-cut and molded into an appropriate size, and (3) a diamond substrate composed of a diamond layer by separating the support substrate from the molded composite substrate. It is common to carry out the separation step and. In such production, it is desired to mass-produce a diamond substrate composed of a diamond layer by forming a diamond layer on a support substrate having a large area and performing a processing step.

Generally, in the forming step, when forming the diamond layer on the supporting substrate, it is necessary to heat the supporting substrate to about 1000 ° C. As a result, stress is generated due to the mismatch of the coefficient of thermal expansion between the diamond layer and the support substrate. In particular, when a diamond layer is formed on a large support substrate that exceeds 2 inches, the diamond layer and the support substrate may warp and cracks may occur in the processing process due to the influence of the above-mentioned stress. As a result, there is a problem that the yield is lowered.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an efficient method for manufacturing a diamond substrate.

In order to solve the above problems, the present inventors have made extensive studies. As a result, they have found that by processing a composite substrate having a diamond substrate layer and a support substrate under predetermined conditions, it is possible to suppress warpage and reduce cracks in the composite substrate after processing, and the present invention has been made. It was completed.

That is, the present invention includes the following inventions.
[Invention 1]
A method for manufacturing a diamond substrate, which includes the following steps.
A forming process in which a diamond layer is formed on a support substrate to form a composite substrate;
A processing process in which a composite substrate is processed at substantially the same temperature as the support substrate in the forming process to obtain a substrate to be processed;
A separation process in which a support substrate is separated from a substrate to be processed to obtain a diamond substrate composed of a diamond layer.
[Invention 2]
The method according to invention 1, wherein the forming step is performed by a CVD method.
[Invention 3]
The method according to invention 1 or 2, wherein the forming step is performed at a support substrate temperature of 500 to 1300 ° C.
[Invention 4]
The method according to any one of Inventions 1 to 3, wherein the processing temperature in the processing step is within ± 200 ° C. with respect to the support substrate temperature in the forming process.
[Invention 5]
The method according to any one of Inventions 1 to 4, wherein the processing temperature in the processing step is within ± 50 ° C. with respect to the support substrate temperature in the forming step.
[Invention 6]
The method according to any one of inventions 1 to 5, wherein at least laser cutting is applied to the diamond layer or both the diamond layer and the support substrate of the composite substrate as processing.
[Invention 7]
The material of the support substrate is at least one selected from the group consisting of graphite, diamond, silicon, silicon carbide, aluminum nitride, sapphire, copper, nickel, silicon nitride, alumina, molybdenum, niobium, tungsten, aluminum, titanium and gallium oxide. The method according to any one of the inventions 1 to 6.
[Invention 8]
In the forming step, a mixed gas of hydrogen, a gas containing carbon atoms, and an NF ₃ gas is used as a raw material gas for forming the diamond layer.
The raw material gas contains 50 to 99.99 vol% of hydrogen with respect to the total amount of the raw material gas, 0.01 to 50 vol% of gas containing carbon atoms with respect to the hydrogen, and gas containing the carbon atoms. The method according to any one of claims 1 to 7, wherein the method contains 0.001 to 1 vol% of NF ₃ gas.
[Invention 9]
A method for manufacturing a substrate to be processed, which includes a diamond layer and a support substrate, including the following steps.
A forming process in which a diamond layer is formed on a support substrate to form a composite substrate;
A processing process in which a composite substrate is processed at substantially the same temperature as the support substrate in the forming process to obtain a substrate to be processed.

According to the present invention, it is possible to suppress warpage and reduce cracks in the composite substrate after processing, so that a high non-defective rate is exhibited. Therefore, the present invention can provide an efficient method for manufacturing a diamond substrate.

It is a figure which plotted the growth rate with respect to N / C of an Example and a comparative example of this invention.

Hereinafter, the present invention will be described. The present invention is not limited to the following embodiments, and the following embodiments have been appropriately modified or improved based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. Is also treated as included in the present invention.

The method for producing a diamond substrate according to the present invention (hereinafter, may be referred to as "method according to the present invention") includes the following steps;
A forming process in which a diamond layer is formed on a support substrate to form a composite substrate;
A processing process in which a composite substrate is processed at substantially the same temperature as the support substrate in the forming process to obtain a substrate to be processed;
A separation process in which a support substrate is separated from a substrate to be processed to obtain a diamond substrate composed of a diamond layer.

[Formation process]
In the forming step, a diamond layer is grown and formed on the support substrate. As a result, a composite substrate having a diamond layer on the support substrate can be obtained.

The material of the support substrate is not particularly limited as long as the diamond layer can be formed on the support substrate. For example, carbons, metals, alloys, ceramics, ceramics-metals and the like can be mentioned. More specific examples include, but are limited to, graphite, diamond, silicon, silicon carbide, aluminum nitride, sapphire, copper, nickel, silicon nitride, alumina, molybdenum, niobium, tungsten, aluminum, titanium, gallium oxide and the like. Not done. Further, these may be a single type or may contain two or more types. Further, in some embodiments, the support substrate may be a laminated substrate composed of a plurality of layers, for example, a first layer made of the above-mentioned material and a first layer made of a material different from the first layer. It may be a multi-layer substrate composed of two layers.

In some embodiments, the supporting substrate may include, but is not limited to, the following materials:
Graphite; diamond; silicon; silicon carbide; aluminum-silicon carbide; magnesium-silicon carbide; aluminum nitride single crystal; aluminum nitride ceramics; sapphire; copper; copper-tungsten alloy; copper-molybdenum alloy; copper-carbon alloy; nickel; nickel -Carbon alloy; silicon nitride; alumina; molybdenum; tungsten; aluminum; aluminum-carbon alloy; titanium.

In some embodiments, the following materials can be exemplified as preferred support substrates;
Silicon; silicon carbide; aluminum-silicon carbide; aluminum nitride; sapphire; copper-tungsten alloy; copper-molybdenum alloy; copper-carbon alloy; silicon nitride; alumina; molybdenum; tungsten; aluminum; titanium.

The shape of the support substrate is not particularly limited, and may be, for example, a circular shape or a square shape. Further, the size of the support substrate is not particularly limited. In some embodiments, when the support substrate is circular, the diameter of the support substrate is preferably 2 inches or more, more preferably 3 inches or more, and 6 inches or more from the viewpoint of upsizing. Is particularly preferable. The upper limit of the diameter is not particularly limited, but from a practical point of view, 10 inches or less is preferable, and 8 inches or less is particularly preferable. In some embodiments, when the support substrate is square, it is preferably 50 mm × 50 mm or more, more preferably 75 mm × 75 mm or more, and the upper limit of the dimensions is 200 mm × 200 mm or less from the viewpoint of increasing the size. Is preferable, but the present invention is not limited to these. Further, in some embodiments, the lower limit of the thickness of the support substrate is preferably 0.05 mm or more, more preferably 0.2 mm or more, and particularly preferably 0.4 mm or more. The upper limit of the thickness is preferably 5 mm or less, more preferably 3 mm or less, and particularly preferably 1.5 mm or less.

In the forming step, the method for growing the diamond layer on the support substrate is not particularly limited, and a known method can be used. As a specific example, it is preferable to use a gas phase growth method such as a pulse laser vapor deposition method (PLD method) or a chemical vapor deposition method (CVD method), but the method is not limited thereto. When the diamond layer is grown on the support substrate, a growth method involving heating of the support substrate is preferable.

In the forming step, it is preferable that the support substrate is subjected to a pretreatment generally applied in advance. Examples of this pretreatment include, but are not limited to, cleaning and drying of the support substrate and arrangement of diamond seed crystals. When a support substrate made of a material other than diamond is used, it is possible to promote the nucleation of diamond by arranging the seed crystal on the support substrate. The existing method may be used for arranging the seed crystals of diamond, for example, a method of performing sonication in an organic solvent using diamond powder, a method of mechanically polishing using diamond powder, or a method of mechanically polishing on a support substrate. A method of forming an intermediate film (intermediate layer) obtained by heteroepitaxially growing Pt, Ir, or the like and arranging a seed crystal on the intermediate film (intermediate layer) is known. It is considered that by undergoing the above treatment, fine diamond particles are embedded on the support substrate, and the particles become seed crystals to promote the formation of the diamond layer. After arranging the seed crystals, it is preferable that the support substrate is washed with water, alcohol or the like, dried, and then subjected to the formation of a diamond layer. When a support substrate made of diamond is used, it is not always necessary to arrange the seed crystals as described above.

In the PLD method, for example, a target containing graphite, amorphous carbon, or diamond is subjected to laser sputtering under an oxygen atmosphere or a hydrogen atmosphere to disperse carbon from the target, and a diamond layer is grown on a support substrate. The pressure inside the furnace, the temperature of the support substrate, and the distance between the target and the support substrate are not particularly limited. Generally, the pressure in the furnace is 1 × 10 ^-4 Pa to 100 Pa, the temperature of the support substrate is 300 to 1000 ° C., and the distance between the target and the support substrate is 10 mm to 100 mm, but the pressure is not limited thereto.

In the CVD method, for example, a support substrate is placed in a CVD growth furnace, and diamond is grown on the support substrate. The growth method is not particularly limited, and for example, a DC plasma CVD method, a hot filament CVD method, a microwave plasma CVD method, a high frequency plasma CVD method, a combustion flame method, an arc jet method, a plasma jet method and the like can be used.

In the CVD method, hydrogen and a gas containing carbon atoms are used as raw material gases. Generally, along with hydrogen, as a gas containing carbon atoms, hydrocarbons such as CH ₄ , C ₂ H ₂ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H ₈ and alcohols such as methanol and ethanol are used. , Use carbon atom-containing compounds such as CO and acetone. These raw material gases may be separately provided in the CVD growth furnace or may be mixed and provided. Further, if necessary, the raw material gas may include a nitrogen source gas, oxygen, and a halogen gas.

In one aspect of the present invention, the raw material gas contains a nitrogen source gas, and NF ₃ is used as the nitrogen source gas. By using NF ₃ gas, the growth rate of diamond can be increased. In this case, hydrogen is 50 to 99.99 vol% of the total amount of the raw material gas, 0.01 to 50 vol% of the gas containing a carbon atom is relative to the hydrogen, and NF is obtained with respect to the gas containing the carbon atom. It is preferable to contain ₃ gas in an amount of 0.001 to 1 vol%, more preferably 0.01 to 1 vol%.

In the CVD method, the pressure inside the furnace and the temperature of the support substrate are not particularly limited. Normally, the pressure inside the furnace is maintained at about 1 × 10 ³ Pa to about 1 × 10 ⁵ Pa, the temperature of the support substrate is maintained at 500 to 1300 ° C., and the raw material gas is applied onto the support substrate to grow (form) diamond. .. In some embodiments, the growth (formation) of a diamond layer by microwave plasma CVD is performed by heating the generated plasma to keep the support substrate at 500-1300 ° C. and depositing active species on the support substrate to deposit diamond. To grow (form).

By the forming step, a diamond layer is formed on the support substrate, and a composite substrate including the diamond layer and the support substrate can be obtained.

[Processing process]
In the processing process, the composite substrate provided with the diamond layer and the support substrate is processed at substantially the same temperature as the support substrate in the forming process to obtain a substrate to be processed. This substantially same temperature depends on the thickness of the diamond layer formed in the forming step and the difference in the coefficient of thermal expansion between the supporting substrate and the diamond, but is usually within ± 200 ° C. of the supporting substrate temperature in the forming step, which is preferable. Is within ± 100 ° C, more preferably within ± 50 ° C.

The processing step may be performed after the forming step, may be performed together with the forming step, or the processing step may be performed together with the forming step, and further processing may be performed after the forming step. Further, in some embodiments, in order to suppress warpage of the composite substrate obtained in the forming step, the temperature of the supporting substrate is set after the forming step until the processing step and during the processing step. Is preferably maintained at substantially the same temperature as the support substrate temperature in the forming step (for example, kept within ± 200 ° C., preferably within ± 100 ° C., more preferably within ± 50 ° C. of the supporting substrate temperature in the forming step). .. The forming process and the processing process may be performed in the same device or in separate devices, but from the viewpoint of efficiency and ease of maintaining substantially the same temperature, they should be performed in the same device. Is preferable. Further, in some embodiments, when the forming step and the processing step are performed in the same apparatus, and particularly when laser cutting is performed as the processing, it is preferable to use the CVD apparatus described later.

By this processing, the diamond layer of the composite substrate or both the diamond layer of the composite substrate and the support substrate are subdivided. The method of subdividing is not particularly limited, and a known method can be adopted. In some embodiments, the process involves at least laser cutting the diamond layer of the composite substrate, or both the diamond layer and the support substrate of the composite substrate.

In some embodiments, the laser is incident on the diamond layer of the composite substrate, or both the diamond layer and the support substrate of the composite substrate, to cut into a desired size and shape.

The laser used for laser cutting is not particularly limited as long as it has a sufficient output and an appropriate wavelength for subdividing the diamond film. From the viewpoint of maintaining the performance of the laser, a solid-state laser is preferable, and from the viewpoint of cutting efficiency, a short-wavelength laser is preferable. Further, a pulse laser is preferable because it can cut the diamond film with a relatively low output and the support substrate is not easily damaged. In some embodiments, preferred lasers include Nd: fiber laser, Nd: YAG laser, Nd: YVO4 laser, high power semiconductor laser and its second harmonic, third harmonic, fourth harmonic and the like. ..

As for the pulse width, since the construction of the optical system is relatively easy and the laser light source is inexpensive, for example, the lower limit is 10 fs or 50 fs, and the upper limit is 1 ms, 100 ns or 500 ps. Specifically, it is preferably 10 fs or more and 1 ms or less, and particularly preferably 50 fs or more and 100 ns or less. The average output depends on the optical system and wavelength, so it cannot be said unconditionally, but the fundamental wave output is preferably 10 W or more. Since the pulse repetition rate depends on the laser system and the like, it cannot be unconditionally specified, but 1 kHz or more and 100 MHz or less are preferable.

For laser scanning, mechanical translation of the optical system or a scanning optical system such as a galvano mirror can be appropriately used. When a galvano mirror is used, it is preferable to use an fθ lens or a corresponding catadioptric system for the condensing optical system.

When laser cutting while forming a diamond layer, it is preferable to recut the same place at appropriate time intervals because the continuous formation of the diamond layer may cause cavities and defects in the cut surface after cutting. .. For this purpose, it is preferable to scan the laser at a relatively high speed. Since the formation rate of the diamond layer is generally within several tens of μm / h, the time interval when recutting the same place is within several hours, preferably within one hour, more preferably within 30 minutes. is there.

In order to improve the cutting speed, a plurality of lasers may be used, or a high-power laser may be divided into a plurality of beam lines and irradiated.

In this processing, a cut is made in the plane direction and the thickness direction of the diamond layer by laser cutting. The cut in the thickness direction may reach a part or all of the diamond layer, or may penetrate the diamond layer and reach a part or all of the support substrate. For example, in some embodiments, the notch in the thickness direction reaches half or more, 80% or more, 90% or more, or all of the thickness of the diamond layer. Further, in some other aspects, the notch in the thickness direction penetrates the diamond layer and is 10% or less, 30% or less, 50% or less, 70% or less, 80% or less, 9 of the thickness of the support substrate. Less than a percentage, or all.

The size of the substrate to be processed is not particularly limited. Although it depends on the size of the diamond layer formed in the forming step, it is usually 2500 mm ² or less, and the lower limit is not particularly limited, but is usually 25 mm ² or more (for example, 2500 mm ² , 900 mm ² , 100 mm ² , 25 mm ^2). ). In some embodiments, the size of the substrate to be machined is 5 mm square to 50 mm square (eg, 5 mm square, 10 mm square, 30 mm square, 50 mm square). The thickness of the substrate to be processed is the thickness of the diamond layer, which is usually 0.01 mm or more, and the upper limit is not particularly limited, but is usually about 1.5 mm (for example, 0.01 mm, 0.03 mm, 0.05 mm). , 0.1 mm, 0.3 mm, 0.5 mm, 1 mm, 1.5 mm). In some embodiments, the thickness of the substrate to be machined is typically 0.1 mm to 1 mm (eg, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm) for both the diamond layer and the support substrate. , 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 1 mm).

In some embodiments, the temperature of the substrate to be processed is lowered. The temperature drop rate is not particularly limited, but is preferably 20 ° C./hr to 500 ° C./hr, and more preferably 100 ° C./hr to 300 ° C./hr. At this speed, cracks due to thermal shock are unlikely to occur, and the production efficiency is moderate.

The substrate to be processed may be subjected to a separation step described later, may be used as it is for various purposes, may be metallized or diced according to the purpose, or the surface of the diamond layer may be polished and smoothed. You may. Since the warp of the substrate to be processed is suppressed by the method of the present invention, the stress at the time of fixing to the polishing machine is reduced, and the flatness and smoothness are improved. Further, in some embodiments, the substrate to be processed can be used as a heat diffusion substrate. Further, in some embodiments, a high thermal conductivity material such as a copper plate or an aluminum nitride ceramic substrate can be attached to the diamond layer of the substrate to be processed.

[Separation process]
In the separation step, the support substrate is separated from the substrate to be processed. As a result, a diamond substrate composed of a diamond layer can be obtained. The support substrate can be separated by a known method. In some embodiments, the separation of the support substrate can be performed by mechanically applying force to the contact surface between the diamond layer and the support substrate, or by other methods of electrochemical etching. Can be done.

The diamond substrate composed of the diamond layers obtained by separation may be metallized or diced according to the purpose, or the surface of the diamond layer may be polished and smoothed. Also, in some embodiments, the diamond substrate can be used as a heat diffusion substrate. Further, in some embodiments, a high thermal conductivity material such as a copper plate or an aluminum nitride ceramic substrate can be attached to the diamond substrate.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited thereto.

In this embodiment, the non-defective rate of the composite substrate was calculated as follows: the laser-cut composite substrate was diced, the amount of warpage per composite substrate after dicing was 30 μm or less, and cracking due to dicing. Those with no chips were judged to be non-defective products, and the number of non-defective products was divided by the total number of composite substrates after dicing and expressed as a percentage. Further, the sum of the warpage amount of the composite substrate after dicing divided by the total number of composite substrates after dicing was calculated as the "average warp amount".

The "warp amount" referred to here is represented by the difference between the highest point and the lowest point on the surface on the support substrate side in the composite substrate after dicing the laser-cut composite substrate. The amount of warpage of the composite substrate after dicing can be measured by performing a three-dimensional shape measurement on the surface on the support substrate side. In this example, the amount of warpage of the composite substrate after dicing was measured using a non-contact three-dimensional measuring device (manufactured by Mitaka Kohki Co., Ltd .: NH-3N).

1. 1. Manufacture of composite substrates

[Example 1-1]
As a support substrate, a substrate having a 2 inch φ silicon substrate (thickness: 1 mm) surface was scratched with diamond powder (average particle size 1 μm), washed with ethanol, and dried by air blow was prepared. This support substrate was placed on a stage in the chamber of the thermal filament CVD apparatus, and the temperature of the support substrate was adjusted to 1000 ° C. Using a mixed gas of H ₂ gas and CH ₄ gas as a raw material gas, a diamond layer having a thickness of 200 μm was formed on a support substrate by a thermal filament CVD method to obtain a composite substrate. Thereafter, the supply of the source gas is stopped while supplying only the H ₂ gas, and the supporting substrate temperature was maintained in the range not exceeding 1000 ℃ ± 20 ℃. At this holding temperature, the diamond layer was cut to a size of 3.5 mm × 3.5 mm by a laser. The amount of cut in the thickness direction of the diamond layer by laser cutting was calculated from the laser focal position and averaged 198 μm.

Here, the laser used is the second harmonic (wavelength 532 nm) of an Nd: YAG laser having an average output of 10 W, and the pulse width is 100 ps. A galvano mirror and an fθ lens were used for laser scanning.

After the laser cutting was completed, the substrate temperature was cooled to room temperature at a cooling rate of 200 ° C./hr. After replacing the inside of the chamber with an inert gas, the composite substrate after laser cutting was taken out. The composite substrate was diced with a dicer along the trace of the laser cut. The average amount of warpage was 4 μm, and the non-defective rate was 83%.

[Example 1-2]
A laser-cut composite substrate was manufactured in the same manner as in Example 1 except that a 4-inch φ silicon substrate (thickness: 1 mm) was used instead of the 2-inch φ silicon substrate, and this was diced. However, the cooling rate after laser cutting was set to 300 ° C./hr. The average warpage amount was 6 μm, and the non-defective rate was 85%.

[Example 1-3]
A support substrate similar to that in Example 1 was prepared except that a 6-inch φ silicon substrate (thickness: 1 mm) was used instead of the 2-inch φ silicon substrate. This support substrate was placed on a stage in the chamber of the thermal filament CVD apparatus, and the temperature of the support substrate was adjusted to 1000 ° C. Using a mixed gas of H ₂ gas and CH ₄ gas as the raw material gas, the diamond layer was laser-cut to a size of 3.5 mm × 3.5 mm while forming a diamond layer on the support substrate by the thermal filament CVD method. The thickness of the diamond layer at the end of formation was 200 μm. The amount of cut in the thickness direction of the diamond layer by laser cutting during formation was 150 μm on average. The supply of the source gas is stopped after the completion of forming, while supplying only the H ₂ gas, and the supporting substrate temperature was maintained in the range not exceeding 1000 ℃ ± 20 ℃. At this holding temperature, the above-mentioned laser-cut portion was further laser-cut. The amount of cut in the thickness direction of the diamond layer confirmed after taking out the composite substrate described later was 207 μm on average, whereby the diamond layer was completely cut and a part of the support substrate was also cut.

The laser and scanning method used are the same as in Example 1-1.

After the laser cutting was completed, the substrate temperature was cooled to room temperature at a cooling rate of 150 ° C./hr. After replacing the inside of the chamber with an inert gas, the composite substrate was taken out. Dicing was done with a dicer along the trace of the laser cut. The average warpage amount was 9 μm, and the non-defective rate was 80%.

[Example 1-4]
A composite substrate after laser cutting was manufactured in the same manner as in Example 1-1 except that the size was cut to a size of 5 mm × 5 mm, and the composite substrate was diced. The average amount of warpage was 12 μm, and the non-defective rate was 79%.

[Example 1-5]
A composite substrate after laser cutting was manufactured in the same manner as in Example 1-1 except that it was cut to a size of 10 mm × 10 mm, and this was diced. The average warpage amount was 20 μm, and the non-defective rate was 75%.

[Example 1-6]
A laser-cut composite substrate was manufactured in the same manner as in Example 1-1 except that a 50 mm square aluminum nitride substrate (thickness: 0.64 mm) was used instead of the 2-inch φ silicon substrate, and this was diced. did. The average warpage amount was 8 μm, and the non-defective rate was 78%.

[Example 1-7]
A laser-cut composite substrate was produced in the same manner as in Example 1 except that a 100 mm square aluminum nitride substrate (thickness: 0.64 mm) was used instead of the 2-inch φ silicon substrate, and this was diced. The average warpage amount was 9 μm, and the non-defective rate was 75%.

[Example 1-8]
A laser-cut composite substrate was manufactured in the same manner as in Example 1-1 except that a 50 mm square silicon nitride ceramic substrate (thickness: 0.64 mm) was used instead of the 2-inch φ silicon substrate. Dicing. The average amount of warpage was 4 μm, and the non-defective rate was 80%.

[Example 1-9]
A laser-cut composite substrate was manufactured in the same manner as in Example 1-1 except that a 4-inch φ sapphire wafer (thickness: 0.53 mm) was used instead of the 2-inch φ silicon substrate, and this was diced. did. The average warpage amount was 24 μm, and the non-defective rate was 78%.

[Example 1-10]
A laser-cut composite substrate was produced in the same manner as in Example 1-1 except that a 100 mm square alumina substrate (thickness: 0.64 mm) was used instead of the 2-inch-silicon substrate, and this was diced. The average warpage amount was 17 μm, and the non-defective rate was 81%.

[Example 1-11]
A support substrate similar to that in Example 1-1 was prepared except that a 4-inch φ SiC wafer (thickness: 0.5 mm) was used instead of the 2-inch φ silicon substrate. This support substrate was installed on a stage in the chamber of the microwave plasma CVD apparatus, and the temperature of the support substrate was adjusted to 1000 ° C. Using a mixed gas of H ₂ gas and CH ₄ gas as the raw material gas, the diamond layer was laser-cut to a size of 3.5 mm × 3.5 mm while forming a diamond layer on the support substrate by the microwave plasma CVD method. .. The thickness of the diamond layer at the end of formation was 200 μm. The amount of cut in the thickness direction of the diamond layer by laser cutting during formation was 170 μm on average. The supply of the source gas is stopped after the completion of forming, while supplying only the H ₂ gas, and the supporting substrate temperature was maintained in the range not exceeding 1000 ℃ ± 20 ℃. At this holding temperature, the above-mentioned laser-cut portion was further laser-cut. The cut length in the thickness direction of the diamond layer confirmed after taking out the composite substrate described later was 206 μm on average, whereby the diamond layer was completely cut and a cut was made in a part of the support substrate.

The laser used was a Yb: fiber laser with an average output of 12 W, a second harmonic (wavelength 520 nm), a pulse width of 1 to 10 ps, and a repeat frequency of 100 MHz. A galvano mirror and an fθ lens were used for laser scanning. Since the laser beam has a narrow field of view that can be scanned, the support substrate was moved together with the stage within a range not exceeding ± 25 mm and laser cut. Since there is concern about the attenuation of the laser beam due to the plasma, the plasma was driven intermittently. The repeat frequency is 10 Hz and the duty ratio is 50%.

After the laser cutting was completed, the substrate temperature was cooled to room temperature at a cooling rate of 150 ° C./hr. After substituting the inside of the chamber with an inert gas, the composite substrate was taken out. Dicing was done with a dicer along the trace of the laser cut. The average warpage amount was 13 μm, and the non-defective rate was 82%.

[Example 1-12]
A support substrate similar to that in Example 1 was prepared except that a 50 mm square copper-tungsten alloy substrate (thickness: 2 mm) was used instead of the 2-inch φ silicon substrate. This support substrate was installed on a stage in the chamber of the microwave plasma CVD apparatus, and the temperature of the support substrate was adjusted to 970 ° C. Using a mixed gas of H ₂ gas and CH ₄ gas as the raw material gas, the diamond layer was laser-cut to a size of 3.5 mm × 3.5 mm while forming a diamond layer on the support substrate by the microwave plasma CVD method. .. The thickness of the diamond layer at the end of formation was 200 μm. The amount of cut in the thickness direction of the diamond layer by laser cutting during formation was 170 μm on average. The supply of the source gas is stopped after the completion of forming, while supplying only the H ₂ gas, and the supporting substrate temperature was maintained in the range not exceeding 970 ℃ ± 20 ℃. At this holding temperature, the above-mentioned laser-cut portion was further laser-cut. The amount of cut in the thickness direction of the diamond layer confirmed after taking out the composite substrate described later was 206 μm on average, whereby the diamond layer was completely cut and a part of the support substrate was also cut.

The laser used was a Yb: fiber laser with an average output of 12 W, a second harmonic (wavelength 520 nm), a pulse width of 1 to 10 ps, and a repeat frequency of 100 MHz. A galvano mirror and an fθ lens were used for laser scanning. Since the laser beam has a narrow field of view that can be scanned, the substrate was moved together with the stage within a range not exceeding ± 25 mm and laser cut. Since there is concern about the attenuation of the laser beam due to the plasma, the plasma was driven intermittently. The repeat frequency is 10 Hz and the duty ratio is 50%.

After the laser cutting was completed, the substrate temperature was cooled to room temperature at a cooling rate of 150 ° C./hr. After replacing the inside of the chamber with an inert gas, the composite substrate was taken out. Dicing was done with a dicer along the trace of the laser cut. The average amount of warpage was 10 μm, and the non-defective rate was 75%.

[Comparative Example 1-1]
After forming the diamond layer, a composite substrate after laser cutting was produced in the same manner as in Example 1-1 except that the substrate temperature was lowered to room temperature (29 ° C.) and laser cutting was performed, and this was diced. The average warpage amount was 37 μm, and the non-defective rate was 23%.

[Comparative Example 1-2]
After forming the diamond layer, a composite substrate after laser cutting was produced in the same manner as in Example 1-1 except that the substrate temperature was lowered to 500 ° C. and laser cutting was performed, and this was diced. The average warpage amount was 30 μm, and the non-defective rate was 35%.

[Comparative Example 1-3]
After forming the diamond layer, a composite substrate after laser cutting was produced in the same manner as in Examples 1-3 except that the substrate temperature was lowered to room temperature (27 ° C.) and laser cutting was performed. However, the diamond layer was crushed during the laser cutting, and a good product could not be obtained.

Regarding Examples 1-1 to 1-12 and Comparative Examples 1-1 to 1-3, the size and material of the support substrate, the cut temperature (support substrate temperature at the time of laser cutting), the cut size, and the composite substrate after dicing. Table 1 shows the average warpage amount and the non-defective product rate.

In Table 1, "-" indicates unmeasured.

From this example, it was found that when the laser cut was performed at substantially the same temperature as when the diamond layer was formed on the support substrate, a good non-defective rate was exhibited. Further, it has been clarified that even when the composite substrate is processed into various sizes, the method of the present invention shows a good non-defective rate by suppressing warpage and reducing cracks and chips during dicing. .. Further, from Examples 1-3, 1-11, and 1-12, it was clarified that a good non-defective rate was exhibited even when laser cutting was performed while forming a diamond layer on the support substrate. As a result, it was shown that the production time can be shortened as compared with the case where the diamond layer is formed on the support substrate and then the laser cut is performed.

2. 2. Evaluation of diamond growth rate due to different types of raw material gas

[Example 2-1]
In this example, a microwave plasma CVD apparatus was used. Further, as the raw material gas, H ₂ gas, CH ₄ gas, and NF ₃ gas were used. As the substrate, a substrate was used in which the surface of the Si substrate was scratched with diamond powder (average particle size 1 μm), washed with ethanol, and dried by air blow.

First, the Si substrate subjected to the above pretreatment was placed in a substrate holder in the chamber, and the inside of the chamber was evacuated. At this time, the pressure in the chamber was set to about 1 Pa.

Next, H ₂ gas was flowed into the chamber from the gas supply port, and after the H ₂ gas flowed in, microwaves were generated from the microwave oscillator to generate plasma in the chamber. After the plasma generation, inflow of H ₂ gas, the pressure in the chamber, and increase the input power, eventually input power to the microwave generator 5500 W, the flow amount of H2 gas is 480 sccm, the pressure in the chamber It was set to 10.7 kPa.

Next, 20 sccm of CH ₄ gas and NF ₃ gas were flowed into the chamber, and the chamber was maintained for about 4 hours with various gases flowing. The temperature of the Si substrate at this time was about 1000 ° C. After the lapse of the above time, a sample in which diamond was grown on the Si substrate was obtained. The inflow of NF ₃ gas is shown in Table 2.

[Comparative Example 2-1]
Samples were obtained in the same manner as in Example 2-1 except that the N source gas was not used.

[Comparative Example 2-2]
A mixed gas of H ₂ and N ₂ (H ₂ : N ₂ = 98 vol%: ₂ vol%, described as "H-N" in Table 1) is used as the N source gas, and the inflow amount of the N ₂ gas is shown in Table 2. Samples were obtained in the same manner as in Example 2-1 except as described above.

[Comparative Example 2-3]
A sample was obtained in the same manner as in Example 2-1 except that N ₂ was used as the N source gas and the inflow amount of the N ₂ gas was as shown in Table 2.

[Comparative Example 2-4]
A sample was obtained in the same manner as in Example 2-1 except that NH ₃ was used as the N source gas and the inflow amount of the NH ₃ gas was as shown in Table 2.

Diamonds were confirmed for each of the obtained samples by the following method. In addition, the growth rate of diamond was calculated and shown in Table 2 and FIG.

(Evaluation of synthetic diamond)
The Raman spectrum of each obtained sample was measured using an invia microscopic Raman spectrometer (manufactured by Renishaw). The evaluation was performed by irradiating the sample with a laser beam of 532 nm and determining whether or not a peak of 1333 cm- ¹ derived from diamond could be detected. As a result of the measurement, a diamond film was confirmed in both Example 2-1 and Comparative Examples 2-1 to 2-4.

(Diamond growth rate)
First, the cross section of the obtained diamond film was observed with an electron microscope, and the film thickness was measured. Next, the growth rate (μm / h) per unit time was calculated by dividing the film thickness by the time required for diamond synthesis (the time from the start of the inflow of CH ₄ gas to the end of the inflow).

In Table 2, N / C is calculated according to the following formula (the same applies to FIG. 1):
N / C = [(N source gas flow rate × number of N atoms per molecule of N source gas) / (flow rate of C source gas × number of C atoms per molecule of C source gas)] × 10 ⁶ .

From the above, it was found that the growth rate of diamond in Example 2-1 was the highest when the ratio of supplied N atoms to C atoms (described as "N / C" in Table 2 and FIG. 1) was about the same. It was. Further, from Comparative Examples 2-3 and 2-4, it can be seen that in order to obtain the same growth rate as that of Example 2-1 it is necessary to increase the N / C to about 3 times or more. That is, it was clarified that the amount of NF ₃ gas was smaller than that of the conventional N source gas, and the growth rate could be increased.

Claims (9)

A method for manufacturing a diamond substrate, which includes the following steps.
A forming process in which a diamond layer is formed on a support substrate to form a composite substrate;
A processing process in which a composite substrate is processed at substantially the same temperature as the support substrate in the forming process to obtain a substrate to be processed;
A separation process in which a support substrate is separated from a substrate to be processed to obtain a diamond substrate composed of a diamond layer. The method according to claim 1, wherein the forming step is performed by a CVD method. The method according to claim 1 or 2, wherein the forming step is performed at a support substrate temperature of 500 to 1300 ° C. The method according to any one of claims 1 to 3, wherein the processing temperature in the processing process is within ± 200 ° C. with respect to the support substrate temperature in the forming process. The method according to any one of claims 1 to 4, wherein the processing temperature in the processing process is within ± 50 ° C. with respect to the support substrate temperature in the forming process. The method according to any one of claims 1 to 5, wherein at least laser cutting is performed on the diamond layer or both the diamond layer and the support substrate of the composite substrate as processing. The material of the support substrate is at least one selected from the group consisting of graphite, diamond, silicon, silicon carbide, aluminum nitride, sapphire, copper, nickel, silicon nitride, alumina, molybdenum, niobium, tungsten, aluminum, titanium and gallium oxide. The method according to any one of claims 1 to 6. In the forming step, a mixed gas of hydrogen, a gas containing carbon atoms, and an NF ₃ gas is used as a raw material gas for forming the diamond layer.
The raw material gas contains 50 to 99.99 vol% of hydrogen with respect to the total amount of the raw material gas, 0.01 to 50 vol% of gas containing carbon atoms with respect to the hydrogen, and gas containing the carbon atoms. The method according to any one of claims 1 to 7, wherein the method contains 0.001 to 1 vol% of NF ₃ gas. A method for manufacturing a substrate to be processed, which includes a diamond layer and a support substrate, including the following steps.
A forming process in which a diamond layer is formed on a support substrate to form a composite substrate;
A processing process in which a composite substrate is processed at substantially the same temperature as the support substrate in the forming process to obtain a substrate to be processed.

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